1. Field of the Invention
The present invention relates to a valve timing adjusting apparatus of an internal combustion engine (hereinafter, referred to simply as the engine) for adjusting an opening and closing timing (hereinafter, referred to as the valve timing) of at least one of an exhaust valve and an intake valve of the engine.
2. Description of the Related Art
Conventionally, a valve timing adjusting apparatus for adjusting valve timing of valves is known. Such an apparatus is provided to a transmission system that transmits driving torque of a crankshaft to a camshaft, where the crankshaft serves as an engine driving shaft and the camshaft serves as a driven shaft that opens and closes the exhaust valve or the intake valve of the engine. The valve timing adjusting apparatus adjusts the valve timing by changing a relative rotational phase (hereinafter, referred to simply as the phase) of the camshaft with respect to the crankshaft, thereby enhancing engine output and improving fuel consumption.
An apparatus that changes the phase of the camshaft through the use of oil pressure is one type of valve timing adjusting apparatus. In the case of using oil pressure, however, it is difficult to control a phase change of the camshaft with accuracy when the oil-pressure control conditions are strict, for example, during an operation under low-temperature circumstances, in a period immediately after engine start-up, etc.
In order to eliminate such an inconvenience, Japanese Patent Laid-Open Publication No. Hei. 10-153104 discloses a valve timing adjusting apparatus that changes the phase of the camshaft by making use of an electromagnetic force of an electromagnetic solenoid instead of using oil pressure. This apparatus, however, changes a phase by converting an electromagnetic-induced displacement of a piston member in the axial direction into rotational motions of the camshaft through a helical mechanism. Hence, when a larger width is given to a phase change, a large displacement in the axial direction is experienced by the piston member. This undesirably increases the size of the apparatus. Further, although this apparatus uses an electromagnetic force of the electromagnetic solenoid during an advancing operation that causes a phase change of the camshaft to an advancing side, it uses a biasing force of a biasing member by switching OFF the electromagnetic solenoid during a retarding operation that causes a phase change of the camshaft to a retarding side. This gives rise to a noticeable change in elastic modulus of the biasing member under low-temperature circumstances or the like, and the accuracy of the phase-change control is reduced. Also, because the phase change during the retarding operation depends on a biasing force of the biasing member, there is a limit to improving a response of the phase change. Moreover, energy is lost during the advancing operation for extra work needed to wind a helical spring used as the biasing member.
The invention therefore has an object to provide a valve timing adjusting apparatus of a compact size, capable of ensuring a width of a phase change of the driven shaft with respect to the driving shaft.
The invention has another object to provide a valve timing adjusting apparatus having an excellent phase change response of the driven shaft with respect to the driving shaft.
The invention has yet another object to provide a valve timing adjusting apparatus capable of constantly and accurately controlling a phase change of the driven shaft with respect to the driving shaft.
According to a valve timing adjusting apparatus of a first aspect of the invention, a first brake portion transmits a first torque to a first eccentric shaft that is off-center from a driven axis. The first eccentric shaft rotates around the driven axis in a direction opposite to the rotational direction of the driven axis. The first eccentric shaft then starts to rotate in a retarding direction relative with respect to a rotating member. Accordingly, a first planetary gear, which is supported on an outside wall of the first eccentric shaft to enable a relative rotation and rotates around the driven axis through engagement with a first internal gear of the rotating member, starts to rotate in an advancing direction together with a first output shaft and the driven shaft engaged therewith relative to the rotating member while rotating in the advancing direction relative to the first eccentric shaft. It is thus possible to change, while the first torque is transmitted, the phase of the driven shaft with respect to the rotating member, that is, the phase of the driven shaft with respect to the driving shaft that rotates the rotating member with driving torque, to an advancing side.
Also, according to the valve timing adjusting apparatus of the first aspect of the invention, a second brake portion transmits a second torque to a second eccentric shaft off-center from the driven axis and rotating around the driving axis, in a direction opposite to the rotational direction thereof. The second eccentric shaft then starts to rotate in the retarding direction relative to the rotating member. Accordingly, a second planetary gear, which is supported on an outside wall of the second eccentric shaft to enable relative rotation and rotation around the driven axis through engagement with a second internal gear of the rotating member, starts to rotate in the advancing direction. The second planetary gear rotates together with a second output shaft and the first eccentric shaft engaged therewith relative to the rotating member while maintaining rotation in the advancing direction relative to the second eccentric shaft. The first planetary gear thus starts to rotate in the retarding direction together with the first output shaft and the driven shaft relative to the rotating member while maintaining rotation in the retarding direction relative to the first eccentric shaft. It is thus possible to change, while the second torque is transmitted, the phase of the driven shaft with respect to the rotating member, that is, the phase of the driven shaft with respect to the driving shaft, to a retarding side.
As has been described, according to the valve timing adjusting apparatus of the first aspect of the invention, a displacement of each of the first and second eccentric shafts, the first and second planetary gears, and the first and second output shafts needed for a phase change of the driven shaft with respect to the driving shaft is obtained from a relative rotation around the driven axis with respect to the rotating member. For this reason, a larger quantity can be secured around the driven axis for the displacement of the foregoing components needed for a phase change of the driven shaft. It is thus possible to reduce the apparatus in size while ensuring a width of a phase change of the driven shaft.
According to a valve timing adjusting apparatus of a second aspect of the invention, one of the rotating member and the first output shaft is provided with a stopper slot that extends arc-wise around the driven axis. Further, the other one of the rotating member and the first output shaft is provided with a stopper protrusion that protrudes into the stopper slot and is allowed to rotate around the driven axis relative to the stopper slot. Hence, by allowing the stopper protrusion to abut against one or the other end portion of the stopper slot, it is possible to limit relative rotations of the first output shaft and the driven shaft with respect to the rotating member. In short, a length of the arc of the stopper slot can limit a width of a phase change of the driven shaft. It is thus possible to set a wider width to a phase change of the driven shaft by forming the stopper slot longer around the driven axis.
According to a valve timing adjusting apparatus of a third aspect of the invention, a first cyclone deceleration mechanism composed of the first internal gear, the first eccentric shaft, the first planetary gear, and the first output shaft, and a second cyclone deceleration mechanism composed of the second internal gear, the second eccentric shaft, the second planetary gear, and the second output shaft are provided adjacently to each other on the driven axis. Hence, the first cyclone deceleration mechanism and the second cyclone deceleration mechanism can be provided so as to superimpose in at least one of a direction parallel to and a direction perpendicular to the driven axis. It is thus possible to reduce the apparatus in size.
According to a valve timing adjusting apparatus of a fourth aspect of the invention, the first torque and the second torque are obtained by making use of electromagnetic forces induced from the first brake portion and the second brake portion, respectively. Hence, because an electromagnetic force is used in either case of causing a phase change of the driven shaft with respect to the driving shaft to the advancing side or to the retarding side, a response of the phase change can be improved. Moreover, by making use of an electromagnetic force that is hardly influenced by operating conditions, such as a surrounding temperature and an elapsed time since the start of the operation, it is possible to constantly and accurately control a phase change of the driven shaft.
According to a valve timing adjusting apparatus of a fifth aspect of the invention, each of the first eccentric shaft and the second eccentric shaft is provided with a function portion fixed thereto so as to rotate together, and each of the first brake portion and the second brake portion includes a solenoid. Also, each of the first torque and the second torque is obtained from a magnetic attraction force induced between the function portion fixed to corresponding one of the first eccentric shaft and the second eccentric shaft, and the solenoid in a switched-ON state included in corresponding one of the first brake portion and the second brake portion. It is thus possible to transmit the first and second torque with a relatively simple arrangement in a reliable manner.
According to a valve timing adjusting apparatus of a sixth aspect of the invention, the solenoid in each of the first brake portion and the second brake portion is provided so as to enable a displacement toward the function portion by the magnetic attraction force and so as to be attracted to the function portion. Because the solenoid is magnetically attracted to the function portion that rotates together with the first or second eccentric shaft, the first or second torque in large magnitude can be readily obtained. Further, each of the first brake portion and the second brake portion is provided with a biasing means for pushing the solenoid in a direction to move apart from the corresponding function portion. This arrangement makes it possible to stop transmission of the first or second torque by releasing the solenoid from the function portion with a biasing force of the biasing means while a magnetic attraction force is lowered by switching OFF the solenoid. As has been described, according to the valve timing adjusting apparatus of the sixth aspect of the invention, it is possible to allow each of the first torque and the second torque to act on their respective function portions only when needed in a sufficiently large magnitude.
According to a valve timing adjusting apparatus of a seventh aspect of the invention, the solenoid in the first brake portion and the solenoid in the second brake portion are formed into cylindrical shapes having different diameters, one of which is provided at an inner radius of the other. It is thus possible to reduce the apparatus in size.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.